The purpose of the proposed studies is to determine the effects of tumor-promoting and cocarcinogenic agents on plasma cell membranes in relation to the mode of action of these agents. Plasma cell membranes will be isolated from rat liver cells, 3T3 cells, SV-40 transformed cells, primary hamster embryo and benzo(a)pyrene-transformed cells. The effect of tumor-promoters such as phorbol myristate acetate, related inactive analogs such as phorbol and other membrane-active agents, including concanavalin A, on the isolated membrane materials will be examined. Changes in the native fluorescence of membrane proteins will be studied. In addition, the fluorescence probe technique employing both hydrophilic and hydrophobic probes will be used. Probes that are cationic as well as anionic probes will be used and special probes will be synthesized for the purposes of this study where necessary. It is believed that the fluorescence probe technique will yield new information concerning the interaction of amphipathic tumor-promoting agents and other membrane-active agents with cell membranes. This supplemental request is for instrumentation only. An ultracentrifuge for the isolation of plasma membranes is the sole purpose of this supplementary application. The ultracentrifuge originally thought available to us is heavily used and is in a poor state of repair. In order to expedite the research under the ongoing grant it is important that we obtain a new machine for our use at all times.